Photon channeling elements, such as optical fibers, waveguides, articulated arms and others, are used extensively in medical laser systems for delivering light from a laser to a site to be treated or to an optical system for shaping or focusing the laser-light for purposes of the treatment. In many such systems the delivery-end of a photon channeling element is connected to a handpiece used by an operator of the system to direct the laser-light. The handpiece may incorporate an optical system for focusing, shaping or further directing laser-light exiting the photon channeling element.
One well-known principle which is used in prior-art arrangements for detecting energy leakage from or damage to the photon channeling element is to monitor the power of laser-light at the delivery-end of the photon channeling element. The monitored power is compared electronically either with power monitored at the entrance-end of the photon channeling element or with a predetermined reference level representative of power delivered by the photon channeling element in an undamaged condition.
One particular problem in measuring power at the delivery-end of a photon channeling element incorporated in a handpiece, of course, is finding sufficient space for a sampling arrangement to divert a portion of the light exiting the optical fiber for measurement purposes. By way of example, prior-art arrangements have included a beamsplitter to divert a portion of the delivered light to a sensor for monitoring. In another arrangement, what might be described as a scraping arrangement, an aperture stop in the path of the delivered light is used for selecting a portion of light to be measured. This latter arrangement is disclosed in U.S. Pat. No. 4,556,875.
Even where space is available in a handpiece for such arrangements, a problem in using such arrangements may result from variations in form or polarization of a beam of laser-light exiting the optical fiber. Such variations result from changes in the form and amount of bends in the optical delivery element which occur as the handpiece is used by the operator. Such variations in form and polarization of an exiting beam could result in significant variations in detected power, even without damage or breakage of the photon channeling element. This in turn, could result in false indication of damage or breakage. There is a need for an arrangement for monitoring power in a beam of light exiting a photon channeling element which is small enough to be accommodated in a handpiece or the like and which is insensitive to geometry and/or polarization variations in the exiting beam.